CN111095057A

CN111095057A - Anti-impact light guide structure

Info

Publication number: CN111095057A
Application number: CN201780094902.8A
Authority: CN
Inventors: 维尔·孔图里
Original assignee: Nanocomp Ltd Oy
Current assignee: Nanocomp Ltd Oy
Priority date: 2017-09-15
Filing date: 2017-09-15
Publication date: 2020-05-01
Anticipated expiration: 2037-09-15
Also published as: EP3682162A1; US11267211B2; EP3682162C0; WO2019053317A1; EP3682162B1; CN111095057B; EP3682162A4; US20200269531A1

Abstract

The light guiding structure (100) has a first major surface (101) and an opposite second major surface (102), the light guiding structure (100) being configured to guide light in the light guiding structure via total internal reflection at the first major surface and the second major surface. The light guiding structure comprises external coupling means (120), the external coupling means (120) being configured to couple light propagating in the light guiding structure out of the light guiding structure through the first main surface and/or the second main surface. The light guide structure comprises two cladding layers (111)₁、111₂) And a core layer (110) sandwiched between the cladding layers, the core layer comprising a core material and the cladding layers comprising a cladding material, respectively. The core material has a higher elasticity than the cladding material, and the core material has a refractive index at the design wavelength that is substantially the same as the refractive index of the cladding material at the design wavelength.

Description

Anti-impact light guide structure

Background

Light directing films and light guide plates are used in various applications, such as in backlights for displays, to direct and redistribute light.

Light may propagate within the light guiding film or light guiding plate by total internal reflection. To couple light out of the light guide, various types of optical microfeatures can be incorporated in or on the light guide structure. Such microfeatures and external coupling devices including them may be susceptible to damage caused by spot size impacts on the light guide.

Local damage to the external coupling device can have a detrimental effect on the operation and/or visual appearance of the light guide and the entire assembly to which the light guide is attached or connected in the device. For example, in the case of a backlight for a display, such damage may appear as a "white spot" of a dark spot, thereby degrading the visual appearance of the display. The susceptibility of microstructures to damage may even increase as the trend continues toward larger and larger displays, for example, in mobile devices.

Disclosure of Invention

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

In a first aspect, a light-guiding structure may be realized, characterized by what is specified in claim 1. The light guide structure has a first major surface and an opposing second major surface and is configured to guide light in the light guide structure via total internal reflection at the first major surface and the second major surface.

The light guiding structure comprises external coupling means configured to couple light propagating in the light guiding structure out of the light guiding structure through the first main surface and/or the second main surface.

The light guiding structure includes two cladding layers and a core layer sandwiched between the cladding layers. The core layer comprises a core material and the cladding layer comprises a cladding material which may be the same. The core material has a higher elasticity than the cladding layer and has a refractive index at the design wavelength that is substantially the same as the refractive index of the cladding layer.

In a second aspect, a manufacturing method can be realized, characterized by what is specified in claim 15. The method may be used to manufacture a light guiding structure according to the first aspect described above.

The method comprises the following steps: forming at least one of the core layer and the cladding layer by applying a curable substance in substantially liquid form on a solid carrier layer; and curing the thus applied substance.

Drawings

The invention will be better understood from the following detailed description read in light of the accompanying drawings, in which:

fig. 1 to 4 show schematic cross-sectional views of various types of light guiding structures with external coupling means;

FIG. 5 shows a schematic cross-sectional view of a backlight module comprising a light guiding structure; and

fig. 6 and 7 show a flow chart of a method for manufacturing a light guiding structure.

Figures 1 to 5 of the drawings are not drawn to scale.

Detailed Description

The detailed description provided below in connection with the appended drawings is intended as a description of various embodiments and is not intended to represent the only ways in which these embodiments may be constructed, implemented or utilized.

Some of the embodiments and examples discussed below may allow, for example, to realize a light guiding structure with external coupling means having a high resistance to the formation of white spots or other types of defects in the external coupling means due to spot size or local impact on the light guiding structure.

Such spot size or local impact may be caused, for example, by an undesired contact occurring between the light guiding structure and another element, such as a display element, to which the light guiding structure is mounted in the device, which is initially separated from the light guiding structure by a small gap. Such undesired contact may occur, for example, during bending of the device. For example, during assembly of the display module, the impact may also be caused by small particles remaining between the light guiding film or plate and another element of the display module to which the light guiding film or plate is attached.

The light guiding structure 100 of fig. 1 has a first major surface 101 and a second major surface 102 opposite the first major surface. In the example of fig. 1, the first major surface and the second major surface are substantially parallel. In other embodiments, the first and second major surfaces of the light directing structure may be oriented slightly differently. The light guiding structure may then for example be wedge-shaped. The light guiding structure is configured to guide light in the light guiding structure by total internal reflection on the first and second major surfaces, as indicated by the arrows representing the light beams 105 in fig. 1.

"light guide" refers to an optical element adapted and designed for guiding light therein, i.e., guiding light within the light guide. "light directing structure" refers, in turn, to a structure that may form part or all of a light guide. The light guiding structure may be formed as a rigid element. Alternatively, the light guide may be formed as a flexible element and/or a bendable element, thereby allowing for a flexible light guide and/or a bendable light guide that may be used, for example, in a bendable display assembly or module.

The "first major surface" and the "second major surface" of the light guiding structure, which are opposite to each other and define the thickness of the light guiding structure, may be considered to be, for example, the lower/bottom surface and the upper/top surface of the light guiding structure. It should be noted, however, that such references to an upward direction and a downward direction or an upper or lower position, as well as the "horizontal" and "vertical" directions discussed below, are to be understood as being defined with respect to coordinates fixed to the light guide structure itself, such that the first major surface is the "lower" major surface and the second major surface is the "upper" major surface. For example, in coordinates fixed to the earth's gravity direction, these surfaces may naturally be located in any direction depending on the position of the light guide plate. Thus, the terms "vertical" and "horizontal" should be understood as auxiliary expressions that do not necessarily coincide with the horizontal and vertical directions in coordinates that are fixed relative to the earth's gravity or any other external coordinates.

The light guide structure comprises a first cladding layer 111 sandwiched between₁And a second cladding layer 111₂With a core layer 110 in between. In the example of fig. 1, the core layer is in direct contact with both cladding layers, and thus without any intermediate layer therebetween. In other embodiments, there may be some intermediate layers between the core layer and one or more of the cladding layers, for example for bonding or other purposes.

"layer" refers to a structural element of a light directing structure that extends two-dimensionally in a "horizontal" direction and has a thickness in a "vertical" direction perpendicular to the horizontal direction that is substantially lower than the horizontal dimension of the layer. Thus, the entire assembly of each layer and the two cladding layers sandwiching the core layer may form a plate-like or sheet-like structure. This structure may also be considered a "membrane".

The light guiding structure further comprises external coupling means 120 configured to couple light propagating in the light guiding structure out of the light guiding structure. Thus, in use, the outer coupling arrangement may again redistribute light received into the light guiding structure out of the light guiding structure, e.g. towards a display such as a Liquid Crystal Display (LCD) element. In other applications, the light coupled out of the light guiding structure may have a different purpose.

As shown in fig. 1, the outer coupling means 120 is configured to couple a portion of the energy of the light beam 105 incident on the light guiding structure to the sub-light beam 106, while the rest of the light energy may be reflected back to the light guiding structure by total internal reflection. The outer coupling efficiency may be uniform throughout the outer coupling device such that the fraction of incident light energy is constant. Alternatively, the external coupling efficiency may vary, i.e. differ at different locations or in different areas of the light guiding structure. For example, where light is received into the light guide structure through an edge surface of the light guide structure, the out-coupling efficiency may be lower near the edge and increase with increasing distance from the edge. This improves the uniformity of the intensity of the external coupling light.

The outer coupling means of the light guiding structure may cover a major part or substantially the entire area of the light guiding structure. In other embodiments, the outer coupling means may be formed only on a part of the area of the light guiding structure or on several separate areas of the area of the light guiding structure.

External connectionThe device may comprise any suitable means enabling said function of coupling light out of the light guiding structure. In the example of fig. 1, the outer coupling means 120 includes a second cladding layer 111 formed on an upper one of the cladding layers₂Is formed on the outer surface 112 of the substrate in the form of surface relief microstructures 121. In the example of fig. 1, the outer surface coincides with the second main surface 102 of the light guiding structure and actually forms the second main surface 102 of the light guiding structure.

By "optical microfeatures" is meant micro-scale structures, patterns, particles, or other types of features that are capable of affecting the propagation of light, at least at a predetermined design wavelength, such that light propagating within the light guiding structure and incident on such one or more optical microfeatures is at least partially coupled out of the light guiding structure. "micro" and "microscale" refer to features having at least some feature sizes in the range of sub-wavelength sizes to tens of wavelengths relative to a predetermined design wavelength for which the light-guiding structure is designed.

The affecting the propagation of light may be based on, for example, refraction, reflection, scattering or diffraction of light interacting with the optical microfeatures.

The plurality of optical micro-features may be arranged in a regular, quasi-regular or irregular distribution in the light guiding structure. In the case of a regular distribution, the plurality of microfeatures may be arranged in a periodic grid or grating, for example. The optical microfeatures may lie substantially in or along a plane that may be oriented parallel to the first major surface and/or the second major surface of the light guide structure, as is the case in the light guide structure 100 of fig. 1. In other embodiments, the optical micro-features may be distributed in or along several different planes, which may be oriented differently from the first major surface and/or the second major surface of the light guiding structure. In other embodiments, the optical microfeatures may be distributed within the outer coupling volume. An example of the latter is shown in fig. 3.

In the example of FIG. 1, the external coupling means 120 comprising microstructures 121 on the second major surface 102 are configured to direct externally coupled light out of the light guide through the second major surface itself. Thus, light is coupled from the light guiding structure to the side of the light guiding structure on which the external coupling means are located. In other embodiments, the external coupling means may be configured to couple light out of the light guiding structure to a side of the light guiding structure opposite to the side where the external coupling means is located. For example, in the case of an outer coupling structure similar to the example of fig. 1 that includes surface relief microstructures on the second or first major surface, the microstructures can direct portions of incident light through the light guide structure and out of the light guide structure through the opposing first or second major surface, respectively.

The microstructures, i.e., structural microfeatures, may include any suitable type of dots, lines, grooves, ridges, etc. In the example of fig. 1, the microstructures are shown as generally pyramidal protrusions. In other embodiments, the structural microfeatures may comprise a structure or pattern having two different height levels, i.e., a binary structure. Alternatively, the optical microfeatures may include a multi-level height variation having a plurality of discrete height levels, or the optical microfeatures may have a continuously or gradually varying height level.

In other embodiments, other types of optical microfeatures may be used, such as scattering, reflecting, or refracting particles distributed within or on one or more of the layers of the light guiding structure. An example is shown in fig. 3.

Light guide structure 300 of fig. 3 differs from that of fig. 1 in that, instead of surface relief microfeatures on the surface of one of the cladding layers, outer coupling means 320 comprises scattering particles 322 distributed within a second cladding layer or upper cladding layer 312. Thus, the second cladding layer serves as an outer coupling volume. Light guiding structures with such scattering particles may be used, for example, to provide diffuse light, i.e. light that is substantially randomly guided into a range of solid angles. In the diagram of fig. 3, this is indicated by arrows indicating a light beam 305 propagating in the light guiding structure 300, and randomly oriented sub-beams 306 leaving outside the light guiding structure, to which randomly oriented sub-beams 306 part of the light energy of the light beam is coupled.

In other embodiments, the outer coupling device may include any suitable other type of optical microfeature. In the vertical or thickness direction, the typical outer coupling means and its optical microfeatures may be positioned embedded within, on or near the first and/or second major surfaces of the light guiding structure.

The core layer 110 includes a core material, and may be entirely formed of the core material. First cladding layer 111₁Including and may be formed entirely of the cladding material. Thus, the second cladding layer 111₂Including and may be formed entirely of the cladding material. The cladding material of the first cladding layer and the second cladding layer may be the same. In other embodiments, the coating materials of different coatings may have more or less different compositions, or the coating materials of different coatings may be completely different materials. Fig. 4 shows an embodiment of a light guiding structure with such a different cladding material.

The core layer 110 core material and cladding layer 111 for at least the design wavelength₁、111₂The refractive indices of the cladding materials of (a) are substantially the same. The entire stack of these three layers can then be used from an optical point of view as essentially one single body or optical element, where the different layers are optically similar. In other words, light may propagate from one layer to another without any substantial reflection or refraction at the interface between the two layers. As long as such conditions are satisfied, the clad materials may have refractive indices slightly different from each other.

The "refractive index" n of a material refers to the ratio of the speed c of light in vacuum to the phase speed v of light in the material:

in fact, each non-ideal material causes at least some loss of light energy propagating in the material. This attenuation effect can be achieved by complex refractive indicesnExpressed, the complex index also takes into account the loss of the imaginary part in the form of the extinction coefficient k:n＝n+iκ

to provide the optical similarity, the materials of the core layer and the cladding layers may be selected such that the real part of the complex refractive index of the core material for the design wavelength deviates from the real parts of the complex refractive indices of the cladding materials of the first cladding layer and the second cladding layer for the design wavelength by 1% or less, preferably by 0.5% or less.

On the other hand, the materials of the core layer and the cladding layers may be selected such that the imaginary parts of the complex refractive indices of the core material for the design wavelength deviate from the imaginary parts of the complex refractive indices of the cladding materials of the first cladding layer and the second cladding layer for the design wavelength by 0.5% or less, preferably by 0.3% or less.

In practice, the refractive index and the complex refractive index are always wavelength dependent, i.e. they may be more or less different for different wavelengths. In the above description, the similarity of the refractive indices of the core and cladding materials relates to their similarity at least at the predetermined design wavelength for which the light guiding structure is designed. This design wavelength refers to the intended wavelength at which the light guiding structure is to operate. The design wavelength may be located in the visible wavelength range or the infrared wavelength range, for example.

Such small maximum deviations in the real and/or imaginary parts of the complex refractive index between the material of the core layer and the material of the cladding layer between which the core layer is sandwiched can keep the interface effect, which light propagating from one layer to the other experiences, sufficiently small.

In case one or more intermediate layers are present between the core layer and the at least one cladding layer, the material or materials of the intermediate layer or layers are preferably selected such that sufficient optical similarity is also obtained between the intermediate layer, the core layer and the cladding layer.

The mechanical properties of the materials of the core layer and the cladding layer are different compared to the optical similarity, since the elasticity of the core material is higher than the elasticity of the two cladding materials.

It is well known that the elasticity of a material affects the rigidity of a body formed from the material, i.e. the ability of the body to resist deformation in response to forces exerted thereon. Thus, in the case of exerting similar forces on two bodies having the same shape and dimensions, one body is formed of a material having a higher elasticity than the other body exhibiting a higher deformation. In general, elasticity can be considered to be related to the stiffness of the material.

The different elastic properties of the core and cladding layers may serve different purposes in the event that an impact is dropped or applied to the light guiding structure. The less elastic cladding layer redistributes the energy of a local, small-sized or point-sized impact into a larger region, while the more elastic core layer absorbs the impact energy by deforming. As a result, the resistance of the optical layer structure to impact-induced defects in the external coupling device may be reduced compared to a light guiding structure having a similar thickness but formed entirely of a single material.

In order to provide said mechanical difference between the different layers, the materials of the core layer and the cladding layers may be chosen such that at least one, and possibly both, of the cladding materials of the first and second cladding layers (which may be of the same material) have a young's modulus which is at least 50% higher, preferably at least 75% higher, than the young's modulus of the core material.

The possibilities of choosing the core and cladding materials are different in order to obtain the appropriate optical similarities and mechanical differences. First, the materials of the different layers may be selected from significantly different materials or types of materials. On the other hand, the mechanical properties of various optical materials can be adjusted by suitable additives that affect the composition and mechanical properties of the material while not substantially changing the refractive index. Thus, materials with different mechanical properties may be substantially the same, but their exact composition may be sufficiently different to obtain the desired difference in elasticity.

The optical properties of the material, such as refractive index and complex refractive index, may be influenced and may be adjusted, for example, by adding colorants and/or suitable nanoparticles to the material. The nanoparticles may be selected to have different optical properties than the bulk material into which they are incorporated, but are sized so as not to cause substantial scattering of light at the design wavelength. One common example of nanoparticles suitable for use as such an additive is TiO₂And (3) nanoparticles.

For example, the mechanical properties, such as young's modulus, of the core and cladding materials can be influenced by selecting monomers or oligomers with different mechanical properties as the base material for those materials. In addition, suitable additives may also be used. For example, for PMMA as the cladding material, a comonomer such as butyl acetate or a plasticizer may be used.

The additive may be added to the material, for example during its manufacture. In the case of a material that may be formed from a curable substance that is initially in liquid form, the additive may be added to the liquid substance before the liquid substance is cured.

At least one of the cladding materials may comprise polycarbonate, polyethylene terephthalate PET, acrylic such as poly (methyl methacrylate) PMMA, or glass. Suitable glass materials are commercially available, for example, under the trade name

Glass、SCHOTT AF

eco, and SCHOTT AS87 eco.

The core layer may comprise, for example, silicone or thermoplastic polyurethane TPU.

In the example of fig. 1, there are a total of three layers in the light guiding structure. Another possibility is shown in fig. 2. Light guide structure 200 of fig. 2 is shown from the light guide structure of fig. 1, and includes two core layers 210₁、210₂And three cladding layers 211₁、211₂、211₃. Each core layer is sandwiched between two cladding layers such that the intermediate cladding layer 211₂As the core layer 210₁、210₂A coating layer of the two. This combination of two core layers and three cladding layers is one example, but not the only possible example, of a light guiding structure comprising a plurality of alternating core and cladding layers. In other embodiments, the light guiding structure may be implemented with any other suitable number of core layers, each sandwiched between two cladding layers. For each core layer and the two cladding layers adjacent to it, the optical similarity and mechanical differences of the materials of the three layers can be set as described above.

The outer coupling device 220 of the light directing structure 200 of fig. 2 may be similar to the outer coupling device discussed above with reference to fig. 1. In other embodiments, instead of surface relief microstructures on the first major surface or the second major surface of the light guide structure, the light guide structure comprising a plurality of alternating core and cladding layers may comprise any other suitable type of external coupling means, such as the external coupling means discussed above with reference to fig. 3.

The multiple alternating core and cladding layers may further improve the impact resistance of the light guiding structure compared to a three-layer structure. On the other hand, the plurality of alternating core and cladding layers may have various core layers, e.g. having mutually different mechanical properties, which may provide more flexible possibilities for the design of the mechanical properties of the light guiding structure.

Light guide structure 400 of fig. 4 may be substantially similar to the light guide structure of fig. 1. However, the first cladding 411₁And a second cladding layer 411₂Are different at least in their precise composition. A core layer 410 and an upper or second cladding layer 411₂Formed on the surface serving as the first clad layer or lower clad layer 411₁On the carrier layer of (a). The carrier layer may include and may be formed entirely of the following materials: for example polycarbonate, PET, acrylic such as PMMA, TPU or glass. Suitable glass materials are commercially available, for example, under the trade name

Glass、SCHOTT AF

eco, and SCHOTT AS87 eco.

In other embodiments, the cladding layer used as one of the cladding layers may comprise the same cladding material as the cladding material of one or more of the other cladding layers of the light guiding structure.

Although not shown in the figures, any of the light directing structures discussed above with reference to fig. 1-3 may also be formed and located on the carrier layer. However, in such embodiments, the carrier layer does not serve as a cladding layer for the light guiding structure and is therefore not part of the actual light guiding structure.

In the case where the carrier layer is used as one of the cladding layers, the thickness of the carrier layer may be significantly higher by one or more than the thickness of the core layer and one or more of the other cladding layers, as shown in fig. 4. This ensures that the entire light guiding structure is sufficiently rigid. On the other hand, during the manufacturing process of the light guiding structure, a sufficient thickness may be required to prevent the carrier layer from being broken or damaged.

Basically, the light guiding structure may have a total thickness of, for example, 0.15mm to 0.5 mm. In many applications, a suitable thickness may be in the range of 0.2mm to 0.3 mm. In case the carrier layer is used as one of the cladding layers, the carrier layer may cover, for example, half or more, even 90% of the total thickness of the light guiding structure.

The outer coupling device 420 of the light guiding structure 400 of fig. 4 may be similar to the outer coupling device discussed above with reference to fig. 1. In other embodiments, instead of surface relief microstructures on the first major surface or the second major surface of the light guide structure, the light guide structure comprising the carrier layer serving as one of the cladding layers may comprise any other suitable type of external coupling means, such as the external coupling means discussed above with reference to fig. 3.

In the above embodiments, as well as other embodiments, the external coupling means of the light guiding structure may comprise essentially any suitable reflective, refractive, diffractive and/or scattering optical means or elements configured to couple light propagating in the light channel out of the light guiding structure. The outer coupling means may be realized as a single continuous structure or means covering the entire area of the light guiding structure or only a part of this area. Alternatively, it may comprise a plurality of separate outer coupling elements or sub-arrangements.

For example, the backlight module 550 of fig. 5 may be used as a backlight device such as a display element of a liquid crystal display LCD element or any variation thereof.

The backlight module 550 includes a light guide structure 500. In the drawing of fig. 5, the light guide structure 500 is shown as having three layers and an outer coupling means 520 having a surface relief microstructure 521, the surface relief microstructure 521 serving as an optical microfeature. Thus, the light guiding structures may be substantially identical to those discussed above with reference to fig. 1 and 4. In other embodiments, the backlight module may include light guide structures according to any of those discussed above, such as those discussed above with reference to fig. 2 and 3.

Backlight module 550 also includes light source elements 560, which may include any suitable one or more light-emitting elements and/or elements, such as one or more LEDs. Basically, any suitable configuration of light source elements suitable for a backlight module may be used.

The light source element 560 is attached to an edge of the light structure and is configured to emit light through its edge surface 503 to the light guiding structure 500. Such light may then propagate in the light guide via total internal reflection at the first and second

major surfaces

501, 502 of the light guide, as indicated by the arrows indicating light beams 505. Upon each interaction with the external coupling means 520, part of the light energy of the light beam is coupled out of the light guiding structure 500 into the sub-beams 506.

The method 600 of fig. 6 may be used to fabricate light guide structures, which may be, for example, according to any of those discussed above with reference to fig. 4.

Method 600 may be performed, for example, in a roll-to-roll (roll) process, where the light guide structure is formed into a long, bendable sheet that can then be cut into discrete light guides. In other embodiments, the light guide component can be directly manufactured as a discrete component.

The method includes applying a solid carrier layer in operation 601, which may, for example, include or be formed from: polycarbonate, PET, acrylic, TPU or glass.

In operation 604, the curable core material is applied in substantially liquid form to the solid carrier layer and then cured in operation 605 to form the core layer. In operation 606, a curable coating substance is applied in substantially liquid form to the solid carrier layer and the core layer already formed thereon. In operation 607, it is cured to form a clad layer.

The curable core and cladding materials may be curable, for example by heat or ultraviolet light. Alternatively, the curable substance may be a solvent-based substance that cures when the solvent evaporates. The curable substance may be selected such that the core layer and the cladding layer comprise those core and cladding materials discussed above with reference to fig. 1.

The application of the initial liquid form enables the layer thickness to be adjusted. In addition, as discussed above with reference to FIG. 1, by adjusting the precise composition of the curable core and cladding materials, adjustments to the mechanical properties of the different layers, as well as possible optical properties, can be achieved.

In the example of fig. 6, the carrier layer forms one of the cladding layers in the finished light guiding structure. Fig. 7 shows another method.

The method 700 of fig. 7 may be used, for example, to fabricate a light guide structure, which may be, for example, any of those light guide structures discussed above with reference to fig. 1 and 3.

The method 700 of fig. 7 differs from the method of fig. 6 in that prior to applying the curable core material, a curable cladding material is applied in substantially liquid form onto a solid carrier layer in operation 702 and cured to form a first cladding layer in operation 703.

The following operations are similar to the corresponding operations discussed above with reference to fig. 6. In

operations

704 and 705, a curable core material is applied in substantially liquid form onto the solid carrier layer and the cladding layer that has been formed thereon, and then cured to form the core layer. In operation 706, a curable coating substance, which may be the same as or different from the curable coating substance applied in operation 702, is applied in substantially liquid form onto the solid carrier layer and the first coating layer and the core layer already formed thereon. In operation 706, it is cured to form a second cladding layer.

The carrier layer may be removed from the completed stack of core layer and carrier layer. Alternatively, the completed light guiding structure may remain on the carrier layer.

In other embodiments, which may be substantially in accordance with any of those methods discussed above with reference to fig. 6 and 7, a plurality of alternating core and cladding layers may be formed sequentially on top of each other. Thus, light guiding structures according to those discussed above with reference to fig. 2 may be manufactured.

In the above method, the external coupling means may be formed in the light guiding structure by any suitable technique.

For example, where scattering, reflecting or refracting particles are distributed in or on one or more of the core and cladding layers, these particles for forming the optical microfeatures may be mixed in the curable substance for the relevant layer prior to application of the curable substance, or added to the applied substance before or after the curing operation.

In the case of surface relief microstructures as the optical microfeatures, the microstructures may be formed, for example, by feeding a layer of curable core or cladding material over a pressure roller having a replication tool attached thereto. Such a replication tool may have a surface texture that corresponds complementarily to the desired microstructure to be formed on the core or cladding layer in question. For example, UV light and/or heat may be applied to the contact area of the curable substance and the pressure roller to cure the layer. Instead of this roll-to-roll compatible method, the layers of curable substance on discrete sheets of pressing tool and carrier layer may be brought into contact with each other to form the microstructures.

Some embodiments are discussed further below.

The light guide structure has a first major surface and an opposing second major surface and is configured to guide light in the light guide structure via total internal reflection at the first major surface and the second major surface. The light guiding structure comprises external coupling means configured to couple light propagating in the light guiding structure out of the light guiding structure through the first main surface and/or the second main surface. The light guiding structure comprises two cladding layers and a core layer sandwiched between the cladding layers, the core layer comprising a core material and the cladding layers comprising a cladding material, respectively. The core material has a higher elasticity than the cladding material and has a refractive index at the design wavelength that is substantially the same as the refractive index of the cladding material at the design wavelength.

In an embodiment, at least one of the cladding materials has a young's modulus that is at least 50% higher than the young's modulus of the core material.

In the embodiment according to the foregoing embodiment, the real part of the complex refractive index of the core material for the design wavelength deviates from the real part of the complex refractive index of the clad material for the design wavelength by 1% at the maximum value.

In an embodiment, which may be according to any of the preceding embodiments, the imaginary part of the complex refractive index of the core material for the design wavelength deviates 0.5% from the imaginary part of the complex refractive index of the cladding material for the design wavelength at a maximum.

In an embodiment according to any one of the preceding embodiments, the core layer is in direct contact with at least one of the cladding layers.

In an embodiment that may be according to any of the preceding embodiments, at least one of the cladding materials comprises polycarbonate, polyethylene terephthalate, acrylic or glass.

In an embodiment that may be according to any of the preceding embodiments, the core material comprises silicone or thermoplastic urethane.

In an embodiment, which may be according to any of the preceding embodiments, the core layer is located on a carrier layer serving as one of the cladding layers, the other cladding layer is located on the core layer, and the cladding materials of the two cladding layers have different compositions.

In an embodiment, which may be according to any of the preceding embodiments, the coating materials of the coating layers have the same composition.

In an embodiment that may be according to any of the preceding embodiments, the light guiding structure comprises a plurality of alternating core and cladding layers.

In an embodiment, which may be according to any of the preceding embodiments, the outer coupling means comprises optical micro features. In an embodiment, the optical microfeatures comprise surface relief microstructures formed on at least one of the surfaces of the core layer and the cladding layer. In embodiments, at least a portion of the surface relief microstructure is formed on the first major surface or the second major surface of the light guide structure.

A backlight module comprises a light guiding structure as defined in any of the above embodiments.

A method for manufacturing a light guide structure as defined in any of the light guide embodiments above, comprising: forming at least one of the core layer and the cladding layers by applying a curable substance in substantially liquid form to the solid carrier layer for each of the core layer and at least one of the cladding layers; and curing the thus applied substance.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

It is to be understood that the benefits and advantages described above may relate to one embodiment, or may relate to several embodiments. The embodiments are not limited to embodiments that solve any or all problems or embodiments having any or all of the benefits and advantages. It should also be understood that reference to "an" item refers to one or more of those items.

The term "comprising" as used in this specification is intended to specify the presence of stated features or acts, but does not exclude the presence of one or more additional features or acts.

Claims

1. A light guiding structure (100) having a first major surface (101) and an opposite second major surface (102), the light guiding structure (100) being configured to guide light in the light guiding structure via total internal reflection at the first major surface and the second major surface, the light guiding structure comprising external coupling means (120), the external coupling means (120) being configured to couple light propagating in the light guiding structure out of the light guiding structure through the first major surface and/or the second major surface,

wherein the light guiding structure comprises two cladding layers (111)₁、111₂) And a core layer (110) sandwiched between the cladding layers, the core layer comprising a core material and the cladding layers comprising a cladding material, respectively, the core material having a higher elasticity than the cladding material, and the core material having a refractive index at a design wavelength that is substantially the same as the refractive index of the cladding material at the design wavelength.

2. The light guiding structure (100) according to claim 1, wherein the young's modulus of at least one of the cladding materials is at least 50% higher than the young's modulus of the core material.

3. The light guiding structure (100) according to claim 1 or 2, wherein the real part of the complex refractive index of the core material for the design wavelength deviates from the real part of the complex refractive index of the cladding material for the design wavelength by 1% at a maximum.

4. The light guiding structure (100) according to any one of claims 1 to 3, wherein an imaginary part of the complex refractive index of the core material for the design wavelength deviates at a maximum from an imaginary part of the complex refractive index of the cladding material for the design wavelength by 0.5%.

5. The light guiding structure (100) according to any one of claims 1 to 4, wherein the core layer (110) and the cladding layer (111) are₁、111₂) Is in direct contact.

6. The light guiding structure (100) according to any one of claims 1 to 5, wherein at least one of the cladding materials comprises polycarbonate, polyethylene terephthalate, acrylic, or glass.

7. The light guiding structure (100) according to any one of claims 1 to 6, wherein the core material comprises silicone or thermoplastic polyurethane.

8. The light guiding structure (400) according to any one of claims 1 to 7, wherein the core layer (410) is located in a carrier layer (411) serving as one of the cladding layers₁) Above, another coating layer (411)₂) On the core layer, and the cladding materials of the two cladding layers have different compositions.

9. The light guiding structure (100) according to any one of claims 1 to 7, wherein the cladding materials of the cladding layers have the same composition.

10. The light guiding structure (200) according to any one of claims 1 to 9, comprising a plurality of alternating core layers (210)₁、210₂) And a coating layer (211)₁、211₂、211₃)。

11. The light guiding structure (100, 300) according to any one of claims 1 to 10, wherein the outer coupling means (120, 320) comprises optical micro features (121, 322).

12. The light guide structure (100) of claim 11, wherein the optical microfeatures comprise surface relief microstructures (121), the surface relief microstructures (121) being formed on at least one of the core layer and the surface (112) of the cladding layer.

13. The light guiding structure (100) according to claim 12, wherein at least part of the surface relief microstructure (121) is formed on the first major surface (101) or the second major surface (102) of the light guiding structure.

14. A backlight module (550) comprising a light guiding structure (560) according to any of claims 1 to 13.

15. A method (600) for manufacturing a light guiding structure according to any of claims 1 to 14, comprising: for each of at least one of the core layer and the cladding layer, forming the core layer and at least one of the cladding layers by applying a curable substance in substantially liquid form on a solid carrier layer; and curing the thus applied substance.